Page 131 - Physics 10_Float

ELECTROMAGNETISM

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Coil Magnetic
B A field

S

Primary
G Secondary Current
Permanent
magnet Magnetic
field
Fig.15.18: Mutual induction
Similarly, when the switch is opened, the galvanometer again
shows a deflection but this time its direction is opposite to
that of the previous case.
The magnetic field of a coil is
identical to the field of a disk
We can explain these observations using Faraday's law of shaped permanent magnet.
electromagnetic induction. When the switch of coil A is
closed, a current begins to flow in the coil due to which
magnetic field is developed across the coil. Some of the
magnetic lines of force of this field start passing through the
coil B. Since current is changing in the coil A, hence number of
magnetic lines of force across the coil B also changes due to
which a current is induced in the coil B in accordance with
Faraday's law. When current in the coil A becomes steady,
number of magnetic lines of force across the coil A also
becomes constant. Therefore, there is no more change in
number of magnetic lines of force through the coil B due to
which induced current in coil B reduces to zero.
Similarly, when the switch of the coil A is opened, the flow of
current through it stops and its magnetic field reaches to zero.
The number of magnetic lines of force through the coil B
decreases to zero due to which current is again induced in it but in
opposite direction to that in the previous case.

15.9 TRANSFORMER
The transformer is a practical application of mutual
induction. Transformers are used to increase or decrease AC

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